In numerical analysis, Simpson’s 1/3 rule is a method for numerical approximation of definite integrals.In Simpson’s 1/3 Rule, we use parabolas to approximate each part of the curve.We divide the area into n equal segments of width Δx. Simpson's 3/8 rule, also called Simpson's second rule requests one more function evaluation inside the integration range and is exact if f is a polynomial up to 3rd degree.